The minister responsible for New Zealand's spy agencies will await the outcome of a quick review of their failings, before deciding whether to launch a deeper inquiry.
The suspected gunman wasn't on any watchlists here or in Australia before carrying out the deadliest mass shooting in the history of both countries.
"We need to know whether there's anything inside those organisations that meant that either they couldn't see what was happening, or they simply didn't see - and if there were things they should have seen that they didn't," Andrew Little told The AM Show on Thursday.
"We need to know that. We need to get an answer to that question fairly soon. The question then is whether we follow that up with a much more deep-seated review."
The initial review will look at the two intelligence agencies - the SIS, which looks at local threats, and the international-focused GCSB - as well as Police, Customs and Immigration.
Little said a "quick answer" was needed on how the gunman wasn't picked up earlier, but expects a fuller, deeper inquiry will be needed.
"This chap was allowed to plan, amass weapons, travel overseas and throughout the country, and in the end he's killed 50 New Zealanders and injured 50 others.
"We need to know whether anything should have been seen; could have been seen; that would have ticked us off to say, 'There's something going on here, we've got to stop this in its tracks.'
"I know that the agencies, through the intelligence they gather, have prevented harmful activities in this country. They do do that. But this didn't happen in Christchurch in the Muslim community, and we want to know why."
Briefings ahead of the attack reportedly focused mostly on threats from Islamic extremists, not against the Muslim community. Just three weeks beforehand, the SIS had assessed the likelihood of a terror attack as low.
Right-wing extremism wasn't mentioned once in 10 years of briefings and annual reports, RNZ reported, despite warnings from the Muslim community.
SIS head Rebecca Kitteridge mentioned it in comments to Parliament's Intelligence and Security Committee in February, but in the context of a "slow but concerning rise" internationally. Most of her comments about extremism and violence concerned Islamic State.
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In the meantime, Little says a group's been set up to deal with the threat from far-right white supremacists that's working around the clock to ensure there are no attempts at a copycat atrocity.
"I think they feel a huge sense of responsibility. I don't think they've done anything other than [what] they could have done," he said.
"But they certainly feel it. They certainly feel that there is a question to answer. They want that question answered."